It's not supposed to be a social network like Facebook. The thing you see when you visit G+ - people microblogging and sharing pics etc - is just a fraction of the whole point of G+.
G+ is Google's social layer. In data terms, it turns people into "first-class citizens" across Google's estate, instead of every project just shoehorning in their own "user" structure. That's why you see G+ in Play reviews, YouTube comments, integrated into email, and so on.